GMC 1999 Envoy Owner's Manual page 284

5. Put the bulb socket into the lamp assembly and twist
it clockwise until it is tight.
6. Put the headlamp assembly back into the vehicle.
Install the two retaining clips.
Taillamps
1. Open the liftgate.
6-34
2. Remove the two screws
from the lamp assembly.
3. Pull the assembly away from the vehicle.
4. Turn the socket counterclockwise to remove it. Push
the tab in while you turn the socket counterclockwise.
5. Holding the base of the bulb, pull the bulb straight
out of the socket.
6. Push the new bulb straight into the socket until
it clicks.
7. Put the socket into the assembly and turn the socket
clockwise until it locks in place.
8. Install the lamp assembly. Install and tighten
the screws.
9. Close the liftgate.
yellowblue